It is common to collect liquids in storage vessels. Such liquids can include oil and other hydrocarbon based fluids, water (fresh or brine), hazardous chemicals, and the like. Vessels can be buried underground such as underground fuel storage tanks used in automotive service stations, or located above ground such as storage tanks used in association with drilling and refining operations in the oil and gas industry. Vessels can be pressurized or vented to the surrounding atmosphere depending upon the volatility and hazards (if any) associated with the collected liquid.
It is often advantageous to monitor the level of liquid present in a vessel. This prevents overfilling as well as indicates when the vessel is approaching an empty condition, allowing additional liquid to be added to the vessel to prevent an interruption in the ability to draw liquid therefrom.
A variety of liquid level indicators have been proposed in the art. An externally mounted liquid level indicator is disclosed in U.S. Pat. No. 3,358,098 issued to Hill. This reference mounts the indicator near the bottom of and through an outer wall of a storage tank to receive hydrostatic pressure from a column of liquid housed within the tank. This pressure is transmitted through a sealing diaphragm to a piston which, in turn, operates a pivotal pointer to provide a relative indication of the height of the column of liquid.
A submerged liquid level indicator is exemplified by U.S. Pat. No. 4,373,388 issued to Kitamura et al. This reference provides a housing with a transversely arranged diaphragm which divides the housing into opposing chambers. The housing is submerged at the bottom of the vessel so that a portion of the liquid enters the lower chamber, while the upper chamber is vented to the external atmosphere. A pressure transducer measures the resulting deflection of the diaphragm to indicate the level of liquid in the vessel.
While these and other prior art approaches may have been found operable, there nevertheless remains a need for continued improvements in the manner in which the level of liquid in a storage vessel can be measured, and it is to these and other improvements that the present invention is generally directed.